Method of decreasing the odor of 1,3-butylene glycol



United States Patent Ofiice 3,489,655 METHOD OF DECREASING THE ODOR OF 1,3-BUTYLENE GLYCOL Edmon A. Peveto, Westlake, La., and James M. Ramey,

Katonah, N.Y., assignors to Celanese Corporation, New

York, N.Y., a corporation of Delaware Filed Dec. 26, 1967, Ser. No. 693,657 Int. Cl. B01d 3/22 U.S. Cl. 20386 Claims ABSTRACT OF THE DISCLOSURE The odor of 1,3-butylene glycol (1,3-BG) is decreased (often referred to as improved) by a final vacuum distillation in a distillation column wherein 1,3-BG of improved odor as compared with that of the feed of 1,3-BG to the column, is taken off as a residual product. An overhead fraction of high-odor 1,3-BG is collected, and a portion of it is returned to the top of the column together with fresh feed stock. The method is carried out while the hot 1,3-BG is in contact only with surface formed of non-catalytic-inducing construction material with respect to its degradation effect on 1,3-BG, specifically stainless steel and/or glass.

The process, which is illustrated in an accompanying fiow sheet, makes possible the consistent production of specification low-odor 1,3 -BG (also specification highodor or commercial-grade 1,3-BG) with a reduction in steam consumption as compared with the unsuccessful efforts to obtain such a product as a side stream from a distillation column which was otherwise essentially the same. The process provides 1,3-BG of such purity that it can be employed in such applications as, for instance, food supplements, especially animal food supplements; as a solvent or liquid carrier for various foods and drugs; and as a humectant for tobacco compositions.

THE INVENTION This invention relates broadly to a method of decreasing the odor of a butylene glycol, specifically 1,3-butylene glycol (1,3-BG).

A conventional method of making 1,3-BG is by catalytically hydrogenating, in the liquid phase, acetaldol which latter is obtained by aldoling acetaldehyde. The product as normally prepared may contain a slight amount of impurities that limit its marketability for certain purposes. All of the following compounds have been identitied in the starting 1,3-BG that has been processed in accordance with the present invention to improve its odor:

Acetaldehyde Butyraldehyde Crotonaldehyde Cisand trans-crotonaldehyde dimers Dimer of butyraldehyde 2,4-hexadienal 2-ethyl-2,4-hexadienal I 1-ethyl-3-methyl-bicyclo (3 .4. 1. -2, 6,8-trio'xaoctane All of the foregoing substances are believed to be odorcausers in 1,3-BG, the last-named compound in the list causing an odor that can be detected in 1,3-BG if present to the extent of only 0.1 ppm. The total concentration of the aforementioned contaminants or impurities is believed to be below 100 ppm. in the 1,3-BG starting material that is further purified by the method of the instant invention. Other odor-causing impurities found in the 3,489,655 Patented Jan. 13, 1970 Z-ethyl-l-butanol (25 ppm.) l-hexanol (50 ppm.) l-butanol (above ppm.)

The present invention is based on our discovery that there are two important and critical factors in improving the odor of 1,3-BG when improvement in odor is attempted by distillation technique: (1) the material of construction of the equipment with which the 1,3-BG comes in contact during distillation; and (2) the point in the distillation column Where the purified 1,3-BG is re moved, specifically as a side-stream product or as a residual product.

More particularly we have found that, although ordinary steel (as distinct from the various stainless steels) are suitable construction materials for equipment used in processing 1,3-BG from the standpoint of corrosion, they are entirely unsatisfactory from the standpoint of producing 1,3-BG with minimum odor. In addition to ordinary steel (so-called carbon steel) which contains about 99% Fe and 1% C, other construction materials that are also unsatisfactory are, for example, ingot iron, wrought iron and cast iron (both white and gray). These irons, ordinary steel, and compounds of iron (more particularly iron oxide or rust) catalyzed some side reactions that occur during the purification of 1,3-BG by distillation. These reactions result in the formation of compounds that impart an undesirable odor to the glycol and make it unsuitable for food and drug uses.

By employing construction materials for distillation equipment that are non-catalytic-inducing at least with respect to reactions that, directly or indirectly, result in the formation of odorous-forming or causing compounds in 1,3-BG, there is obtained purified 1,3-butylene glycol having an improved odor. Examples of such non-catalytic-inducing construction materials, are glass and the various stainless steels. It will be understood, of course, that the entire equipment need not be made of, for instance, glass and/or stainless steel, but only that portion (e.g., in the form of a liner for a distillation column or as trays for such a column) which is in contact with the 1,3-BG being processed.

The present invention provides a process for producing 1,3-butylene glycol of improved odor and taste. By carrying out the final distillation so that the hot glycol is not in contact with surfaces or oxidation products thereof (e.g., carbon-steel surfaces and iron oxides) that can cause degradation of the glycol and/ or objectionable side reactions, there is obtained a purified 1,3-butylene glycol that is so improved in purity as compared with the typical commercial product that it can be employed in such application as, for instance, food supplements, especially animal food supplements; as a solvent or liquid carrier for various foods and drugs; or as a humectant for tobacco compositions.

Typical of the results obtained when the final distillation is carried out in a distillation column wherein its construction material is of the kind hereinbefore described, specifically stainless steel, as compared with commercial 1,3-BG wherein the hot glycol is in contact with carbon steel surfaces in all distillation columns, are the following:

Odor Taste Commercial 1,3-BG product 51. 0 Improved.

The" odor was rated by a panel of six experts (usually only four are employed )"according' to the following rating system:

Numerical value The standard, procedure by which odor and taste of 1,3-BG are determined will be described later herein.

The foregoing tabulated information shows the marked improvement in odor (also an improvement in taste) that f is obtained when the final distillation is carried out in a stainless-steel distillation column and wherein other surfaces with which the hot glycol comes into contact also are made of stainless steel. A still further improvement in odor is obtained when purified 1,3-BG is removed as a residual product from the bottom of the distillation column rather than as a side stream.

The invention will now be described with particular reference to the single figure of the accompanying drawing, which is a flow sheet illustrating how the method of the invention can be carried into effect.

Specification or conventional grade high-odor 1,3- butylene glycol is pumped through conduit into a stainless steel (s./s.) distillation tower or column 12 at the rate of about 7 to 8 gallons per minute (g.p.m. or g./m.). The source of the feed l,3-BG is a side stream from a distillation column for the production of the aforementioned conventional grade of 1,3-BG. The stainless steel used in constructing the tower 12 is 304 and 410 s./s.

The height of the distillation column is a function of the number of trays required to make the desired separation, while the width or diameter depends upon the desired production rate. Hence the ratio of column height to width is not a critical factor within the broad aspects of practicing the method of the present invention. In the apparatus illustrated in the flow sheet of the accompanying drawing, the tower or column 12 is shown as being provided with five sieve trays 14, 16, 18, and 22, which are made ofstainless steel and spaced equidistant from each other. With this number and kind of trays, a column having a height which is, for example, about 7 times its diameter has been found to be effective in practicing the method at the production rates hereafter described.

It is contemplated that the design of the tower and of the, trays, and also the operating conditions, may be adjusted so that effective purification of the feed to the column could be obtained with a lesser or a greater number of trays than the five trays shown in the drawing. Instead of sieve-tray columns, one may also use columns packed with packing material such, for instance, as glass, stainless steel or certain types of ceramic materials in ball, ring or other suitable form. Pulsed-type extractors for effecting the separationof odor-causing impurities also may be employed.

' The distillation column illustrated in the drawing is shown as being provided with 'a narro'wbottom section 24in which"four vertical stainless-steel ballles, 2 inches wide and} feet long (as shown), are installed. These baflles'prev'e'nt vortex formation that otherwise would occur due to the high circulation rate at whichthe residue is'pumped from the afo rementionedsection 24 by means oftherecirdulating pump 26 through the conduit 28 (from which a portion is withdrawn as hereafter described)" to'the lower portion of the heat exchanger 01 reboiler 30l From the upper portion of the said heat exchangerthe pzirtly vaporized residue passes through the conduit 32 back to the base of the tower which it enters at the point designated as 34. The temperature of 6" at th P Rin'the base of he ow r s ab 290'F,"" v

It is not essential that the section 24 of column 12 be narrower than the diameter of the said column as is illustrated in the drawing. Instead it can be of the same diameter as that of column 12.

The high-odor 1,3-BG feed stock enters the column 12 through the conduit 10 at a point just above tray 22 and then flows downwardly from one tray to another while being heated by the passage of hot vapor rising upwardly through the :trays. The feed is stripped of low boilers during its passage over and through the five trays. The stripped stock then falls to the liquid level in the tower which is just below point 34 where the conduit 32 carrying recirculated, partly vaporized, residual 1,3-BG enters the tower. The residue drawn otf from the base of the tower through the narrow bottom section 24 is recirculated as described in the second paragraph immediately preceding at the rate of from about 250 to 300 g.p.m., more particularly, about 275 g.p.m.

The heat exchanger or reboiler 30 is typically a shelland-tube type of exchanger wherein the residue is partially vaporized by steam at a suitable pressure. The pressure of 240 psi. indicated in the accompanying drawing with reference to steam entering this reboiler is that of the steam-generating plant with which the reboiler is tiedin. The line steam pressure in the area of the reboiler is actually about 220 psi. The steam pressure may be considerably lower in the reboiler. The condensate from the condenser is returned to the boiler house or to other process units through a condensate return line.

The size of the reboiler 30, as with other apparatus used in practicing the method of this invention, is a function of unit rate requirements and also, in some cases, the availability of existing equipment. It is not a critical factor in the operability of the method. Illustrative of the size of a suitable reboiler that has been found to be satisfactory in carrying the invention into effect at the unit rates herein set forth is one which is about 2 feet in diameter and about 6 or 7 feet long, and wherein the tubes comprise an area of about 450 square feet. Both the bonnet heads and the tube sheets and tubes are constructed of a non-catalytic-inducing construction material, specifically 304 s./s. The residue flows through the tubes, and does not contact any part of the heat exchanger that is built of carbon steel (c./s.).. The shell thatforms the jacket is made of c./s. with suitable nozzles for the entrance of steam and the withdrawal of condensate. The shell also has suitablebaflles to promote better steam distribution in the exchanger.

It is probable that most of the vaporization of the residual 1,3-BG entering reboiler 30 that takes place occurs in said reboiler. However, there also may be further vaporization or flashing of unvaporized liquid when the stream from the reboiler enters column 12 at the point 34, especially since the column is operating under high vacuum. The hot vapors from both sources pass upwardly through the sieve trays and thus heat and strip the downcoming 1,3-BG feed to the column.

The temperature of the vapors at the top of the column is about 280 F. They exit from the column at the point 36 being carried through the conduit 38. which terminates at the bonnet head of the condenser-40 .which also'is'o-f the shell-and-tube type. Since it is not essential that this condenser be made of a non-catalytic-inducing construction material, the bonnet,-tube sheets and shell of the condenser are all made of carbon steel. a

The outlet of the condenser 40 (in this case,'the bot tom) is connected to a flanged opening 42 on the top of the receiver 44. The shell of the condenser, is' provided with nozzles for inlet and outlet 'water. The'hot yapor from the conduit enters the bonnet of condenser 40 and passes into the c./s. vertical tubes positioned inside the condenser, and which are cooled on the outside by the cold water that enters the bottom of the condenser at46, The water leaves the top of the condenser at 48.

The receiver 44, 'which is mounted in a horizontal position, is constructed of carbon steel throughout. It has a flanged opening at the top adapted to receive the condenser 40. It also has additional nozzles for a vacuum connection, a pressure gauge or indicator (P.I.), and a pump-conduit connection.

A liquid level of specification (high-odor) 1,3-BG is maintained in receiver 44 through suitable instrumentation (not shown). Pump 50 recirculates some of this 1,3-BG through conduit 52 back to the tower 12 at a suitable rate, e.g., about 2 g.p.m. This recirculated 1,3-BG, the temperature of which is about 130 F may be fed directly into the tower onto top tray 22; or, as indicated in the drawing, it may be introduced into the feed conduit carrying the primary feed of high-odor 1,3-BG to the tower 12 at a point just above tray 22. The recirculated 1,3-BG serves to provide the desired reflux to aid in stripping the odorous materials from the low-odor 1,3-BG product. The column temperature is established by the absolute pressure (vacuum). The reflux (recirculated 1,3-BG) has some effect on the temperature and pressure of the column but is not used as a means of controlling the temperature.

The excess of high-odor 1,3-BG in receiver 44 over that amount which is recirculated to the tower 12, as described in the preceding paragraph, is pumped to storage at a suitable rate, e.g., at about 1.5 g.p.m.

A description previously has been given of the manner in which the residual or low-odor 1,3-BG is pumped by pump 26 from the base of the tower 12 through the narroW bottom section 24, thence through the conduit 28 (from which a portion is withdrawn) to the heat exchanger or reboiler 30. After passing through this heat exchanger the residue is returned through the conduit 32 to the tower at the point 34.

At a take-off point 56 on conduit 28 residual 1,3-BG is drawn off at a suitable rate, e.g., 5.5 g.p.m., passing through conduit 58 to suitable cooling means, for instance (as illustrated) to the bonnet of cooler 60. A cooler of the same general design as that of condenser 40, but with a different construction material in a certain area, has been found to be satisfactory. More particularly, with the exception of the shell which is made of carbon steel, the entire exchange or tube area of this cooler is constructed entirely of 304 stainless steel. The stainless steel tubes positioned inside the shell of the cooler 60 are cooled on the outside by water that enters the bottom of the said cooler at 62. The water leaves the top of the cooler at 64. The outlet of the cooler 60 (i.e., the bottom as in condenser 40) is connected to a flanged opening 66 on the top of the receiver 68. This receiver differs from receiver 44 only in that it is made entirely of 304 stainless steel. It has the same number of nozzles for the same types of connections as does receiver 44.

Pumps 70 pumps the desired product, 1,3-BG of low odor and taste, at a temperature of about 100 F. through conduit 72 to storage at a constant rate, e.g., at about 5.5 g.p.m. The parts of this pump that are in contact with the 1,3-BG also are made of stainless steel.

For conciseness, the following recapitulation of typical flow or unit rates mentioned in the foregoing descrip tion and/ or set forth in the accompanying flow sheet are given:

Approximate gallons per minute Residue product (i.e., low-odor 1,3-BG) to storage 5.5 Distillate (i.e., high-odor 1,3-BG) to storage 1.5 Total fresh feed charged to distillation column 7.0 Reflux condensate returned to distillation column 2.0

The storage tanks to which the aforementioned lowodor and high-odor 1,3-BG are discharged, as well as the connecting lines thereto and therefrom, can be made of construction materials that need not have a non-catalyticinducing degradation effect on 1,3-BG at the temperature at which the latter is in contact with the distillation column. For instance, the lines or tanks can be made of carbon steel. Of course, if desired, they can be made of, for example, stainless steel, or of carbon steel or other steel, or other metal, lined with glass or other material that has the above-described non-catalytic-inducing effect.

From the foregoing description it will be noted that the portion of this system that is directed to the production of low-odor 1,3-BG, and with which the said 1,3-BG does or might come in contact especially at elevated temperatures, is constructed entirely of a non-catalyticinducing construction material, specifically stainless steel. Instead of 304 or 410 stainless steel to which reference has been made in the foregoing description, and the compositions of which are given in standard reference books, one may use other commercially available stainless steels including those described in, for example, the Handbook of Chemistry and Physics, 44th Edition, 1962-1963, published by The Chemical Rubber Publishing Company, Cleveland, Ohio. Glass, quartz, fused silica and similar materials may be used separately or conjointly with stainless steels as a construction material. Glass-lined vessels and conduits are useful. Other construction materials that are the equivalent of those just mentioned in their non catalytic-inducing characteristics, with respect to 1,3-butylene glycol degradation and/or the occurrence of undesirable side reactions, also are contemplated. The important and critical factor in obtaining 1,3-butylene glycol having minimum odor is that its purification (if, as here, by distillation) should be effected out of contact with metallic iron, including carbon steels, or iron compounds such as rust.

The entire system as illustrated in the flow sheet of the accompanying drawing is operated under vacuum. A vacuum, i.e., reduced pressure, of less than 10 mm. Hg can be used if desired; but, as hereafter indicated, higher pressures are satisfactory.

Any suitable means for providing this vacuum can be employed. For example, the vacuum can be produced, as illustrated in the drawing, by a steam-operated jet system comprising a first-stage jet 74, an intercondenser 76, and a second-stage jet 78. The intercondenser is used to condense the steam and some process condensables from the first-stage jet. The second-stage jet, which is attached to the intercondenser, provides a lower vacuum than otherwise would be possible, and also exhausts the non-condensables from the system.

The exhaust steam from jet 78 escapes through an exhaust head 80, the function of which is to reduce the velocity of the escaping steam and thereby reduce the noise level. Condensate formed in the exhaust head flows down through the conduit 82 to a hot well 84 or to a sewer. High-pressure steam is used to operate both jets.

The intercondenser 76 uses a spray of cold water to condense vapors from the first-stage jet 74. The water from the intercondenser flows down a barometric leg 86 to the hot well 84. This barometric leg has to be over 34 feet in height in order to let the water flow from the leg to the hot well. The water from the hot well overflows into a drain and thence to disposal.

It is preferred to operate the 1,3-BG purification system at as low a pressure as possible in order (a) to keep the steam pressure (hence also the temperature) required at a low point; and (b) to keep the process temperature at a low level so that there will be minimum degradation of 1,3-BG in the reboiler 30. For example, in a purification system such as that illustrated in the accompanying drawing satisfactory results have been obtained by operating the system under a reduced pressure from about 0.5 to about 2.0 p.s.i abs. and, more particularly, about 1.0 psi. abs. (2.0 p.s.i.'=5l.7 mrn. Hg=51.7 torr).

The system is operated under a reduced pressure or vacuum which, from a practical stand-point, is substantially constant throughout the system. However, during the course of the operation there may be some slight variation from the desired maintainable constant pressure, for instance'up to about 1.0 p.s.i. abs.; and such slight variations are contemplated within the term substantially constant as used above with reference to reduced pressure. The use of substantially higher steam pressure (hence temperature also) has the disadvantage that it may cause degradation of 1,3-BG, especially in the reboiler, thereby resulting in lower unit efiiciency and/or additional formation of odor-causing impurities.

In prior attempts to make low-odor 1,3-butylene glycol, a side stream of 1,3-BG was taken off at a point jr1st below tray 14 thrOugh a conduit leading to a knockout tank or entrainment separator and which was provided with means for removing droplets of liquid that were carried over with the vaporous 1,3-BG. The drop lets that fell to the bottom of this separator were carried therefrom by a conduit (provided with a U-shaped bend to form a liquid seal between the distillation tower and the entrainment separator) back to tower 12. The vapors from the entrainment separator were then condensed, collected and pumped to storage in exactly the same manner as hereinbefore described with reference to the cooling and collection of 1,3-BG when liquid 1,3-BG is taken from residual 1,3-BG at take-off point 56 on conduit 58 and passed into cooler 60.

By the procedure just described, where a sidestream product was taken off just below the bottom tray, it was found to be impossible to produce consistently a low-odor 1,3-BG. The present invention has solved this problem and obviated the difiiculty. An additional economical advantage accruing from the method of this invention is that, by taking off the 1,3-BG as a residual product rather than as a side stream, there is obtained a saving in steam consumption of about 1500 lbs/hr. or more.

Odors of feed and of products under typical operating conditions such as have been previously described and illustrated in the flow sheet of the accompanying drawing are as follows:

Stream Odor 2 Feed to tower 12 22.0 Overhead from tower (i.e., product from receiver 44) 3.0 Residue from tower (i.e., product from receiver 68) 51.0

Both the feed to the distillation tower and the overhead product meet all the specifications for normal (high-odor) grade of 1,3-butylene glycol.

2 Odor-rating scale:

-None 1.0Barely 2.0'Faint 3.0Distinct 4.0Strong The test is amplified by giving fractional ratings to odors rated less than 1.0, eg, 03; also, sometimes, by giving fractional ratings to odors intermediate those rated in Whole members, e.g., 2.5 for an odor rated more broadly between 2. and 3.0

The odor and taste qualities of 1,3-BG are determined in accordance with a standard, unpublished procedure adopted for comparing the intensity of the odor and taste of 1,3-butylene glycol with that of an acceptable standard. The sample and standard are evaluated by a test panel of three or more individuals. For the odor determinations aqueous solutions, by volume, of the sample and of the standard in especially prepared, odor-free, distilled water are formulated in 100 ml. cylinders and poured into 4-ounce, narrow-mouth bottles. Both the cylinders and the bottles are cleaned with cleaning solution and well rinsed the testers observations and determines the average score for each sample and standard.

In the taste procedure a clean, glass medicine dropper is employed to obtain a sample of the material prepared for the odor procedure as described above. One drop of the material is then placed on the back of the tongue, and the degree of taste estimated as stated above with respect to the odor procedure.-

It is to be understood that the foregoing detailed description is given merely by way of illustration, and that many variations may be made therein without departing from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The continuous method of decreasing the odor of 1,3-butylene glycol (1,3-BG) that has an objectionably high odor which comprises:

(A) continuously charging said high-odor glycol to the upper portion of a distillation column wherein it is heated at a temperature sufiiciently high to evolve vapors therefrom; v

(B) continuously removing vapors of 1,3-BG from the top of said column, and continuously condensing said vapors to yield 1,3-BG having a higher odor than the 1,3-BG initially charged to said column;

(C) said high odor 1,3-BG being charged to the upper portion of the distillationcolumn and wherein it flows downwardly through the column over a series of sieve trays positioned at spaced intervals in the said column while vapors of 1,3-BGv are rising upwardly in the column in contact with the downwardly moving 1,3-BG; and a portion of the 13-86 condensate from step (B) is continuously returned to the upper portion of the said distillation column;

(D) continuously (a) withdrawing residual 1,3-BG from the base of said column, (b) passing a portion of the withdrawn residual 1,3-BG through a reboiler wherein it is partially vaporized by heat exchange, and (c) returning to the base ofsaid column, at a point substantially above that at which the said residual 1,3-BG is being withdrawn, the portion of said residual 1,3-BG that has passed through said reboiler;

(E) continuously passing another portion of the withdrawn residual 1,3-BG through a cooling means; and

(F) collecting the cooled 1,3-BG having a lower odor than the feed 1,3-BG charged to the distillation column;

said method being carried out under reduced pressure and while the hot 1,3-BG is in contact only with surfaces formed of non-catalytic-inducing construction material with respect to its degradation effect on 1,3-BG.

2. The continuous method as in claim 1 wherein the surfaces formed of non-catalytic-inducing construction material are stainless steel surfaces.

3. The continuous method as in claim 1.Wherein the surfaces formed of non-catalytic-inducing construction material are glass surfaces.

. 4. The continuous method as in claim 1 wherein the method is carried out under a reduced pressure within the range of from about 0.5 to about 2.0 p.s.i. absolute.

5. The method as in claim 1 wherein theportion of the 1,3-BG condensate from step (B) that is continuously returned to the upper portion of the distillation column is admixed with fresh 1,3-BG feed that is continuously being charged to the said column. 1

6. The method as in claim 1 wherein a portion of 1,3-BG condensate from step (B) is continuously returned to the upper portion of the distillation column; the portion of the residual 1,3-BG that is'con'tinuously passed through a cooling means as is specified-in step (D) is withdrawn from the conduit carryingresidual 1,3-BG, withdrawn from the bottommost portion" of the distillation column, enroute to the reb'oilerf'and the 'hot 1,3-BG is in contact only with surfaces formed of stainless steel and/or glass.

7. The method as in claim 6 wherein the temperature of the 1,3-BG is approximately 280 F. at the top and approximately 290 F. at the bottom of the distillation column.

8. The method as in claim 1 wherein high-odor 1,3-BG is continuously charged at the rate of about 7 volumes per minute to the upper portion of a distillation column wherein said 1,3-BG passes downwardly through the column over a series of distillation trays positioned at spaced intervals in said column while vapors of 1,3-BG are rising upwardly in the column in contact with the downwardly moving 1,3-BG, the temperature of the 1,3-BG at the top of the column being approximately 280 F.; continuously condensing said vapors to yield 1,3-BG having a higher odor than that of the 1,3-BG initially charged to said column; continuously returning a portion of this condensate-to the upper portion of said distillation column at the rate of about 2 volumes per minute while continuously pumping to storage another portion of this condensate at the rate of about 1.5 volumes per minute continuously (a) withdrawing residual 1,3-BG at a temperature of about 290 F. from the bottom of said column, (b) passing a portion of said residual 1,3-BG through a reboiler wherein it is partially vaporized by indirect heat exchange with high-pressure steam and (c) returning to the base of said column, at a point substantially above that at which the said residual 1,3-BG is being withdrawn, the portion of said residual 1,3-BG being passed through said reboiler continuously withdrawing, at the rate of about 5.5 volumes per minute that portion of the residual 1,3-BG which is passed through said cooling means from the conduit carrying residual 1,3-BG from the bottommost portion of the distillation column enroute to the reboiler; continuously cooling, collecting and pumping to storage said residual 1,3-BG at the rate of about 5.5 volumes per minute, said 1,3-BG having a lower odor than the feed 1,3-BG charged to the distillation column; the method being carried out under reduced pressure with the hot 1,3-BG in said column and in the reboiler system connected thereto being in contact only with apparatus surfaces formed of glass or'stainless steel.

9. The method as in claim 8 wherein the reduced pressure is from about 0.5 to about 2.0 psi. absolute.

10. The method as in claim 9 wherein the reduced pressure is about 1.0 psi. absolute.

References Cited UNITED STATES PATENTS 1,881,718 10/1932 Laurie 203-86 2,368,669 2/ 1945 Lee et al. 203-90 X 2,629,686 2/1953 Grosser 203-91 X 2,691,048 10/1954 Francis 260-637 X 2,768,214 10/1956 McKinley et al 260-637 3,132,987 5/1964 Sinex 159-31 3,197,386 7/1965 Lau 203-86 X 3,232,996 2/ 1966 Graham et al. 260-637 3,304,247 2/ 1967 Hoffman 260-635 X FOREIGN PATENTS 729,841 5/1955 Great Britain.

927,809 6/ 1963 Great Britain.

990,612 4/1965 Great Britain.

NORMAN YUDKOFF, Primary Examiner F. E. DRUMMOND, Assistant Examiner US. Cl. X.R. -32; 202-173; 203-91, 98; 260-637 

